Mechanized method and apparatus for releasing stranded ships



May 12, 1959 J. c. MYERS MECHANIZED METHOD AND APPARATUS FOR RELEASING STRANDED SHIPS Filed April 5, 1957 INJECTION 8 Y8 TEM Wafer Line .5 WWW MM w m W m m w ,A w

United States Patent ME(JI-IANIZIID METHOD AND APPARATUS FOR RELEASING STRANDED SHIPS Jacob C. Myers, Panama City, Fla.

Application April 5, 1957, Serial No. 651,116

Claims. (Cl. 11451) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to the release of marine vessel-s which have stranded upon a shoal of sand, mud, or the like and more particularly to an improved method and apparatus for releasing and refioating vessels so stranded.

Heretofore, efforts to free stranded vessels which could not be moved by the static pull of a tug or other tow ship have been directed towards overcoming static friction or. suction by expedients such as shifting the center of gravity of the vessel to impart a rocking. movement thereto, producing a flow of water along the hull to scour out a portion of the offending bottom, surging on .the tow line by the tug, and the like. Surging by a tug is quite critical and generally results: in a parted tow line while the other expedients are extremely difficult to practice effectively.

It is the primary object of the invention to provide a relatively simple method and apparatus for releasing stranded marine craft.

Another object of. the invention is to: provide a mechanical system as distinguished from seamanship for releasing craft so. stranded.

These and other objects of the invention are obtained by imparting to a taut tow line secured to a stranded vessel a series of very' high momentary stresses or tensions for overcoming the static friction between the stranded hull and the bottom.

In accordance with the invention a tow line or cable secured to a stranded vessel is held under heavy strain by a tug or other source of power and while so held is periodically subjected to tension surges having a magnitude at least equal to and preferably several times greater than the magnitude of the steady tension maintained by the tug. In the preferred form of the invention the periodic tension surges are produced by an explosion powered underwater jet or reaction device.

The invention as well as other objects and advantages thereof will be better understood from the following description of a preferred embodiment, reference being had to the accompanying drawing in which:

Fig. 1 is a diagrammatic illustration of a tow system embodying the method of the invention; and

Fig. 2 is a 'conventionalized showing of a power plant suitable for applying periodic thrusts to a tow line.

The present invention is grounded on the well-known fact that static friction is considerably greater than dynamic friction and achieves its great advantage by concentrating the towing power in overcoming static friction. The primary advantage of the invention is that it provides a method whereby a greatly amplified towing force is obtained from a given available average power, by exerting a series of extremely high instantaneous power pulses. When these power pulses or tension surges ice are imparted to a taut tow line at a relatively high frequency, e.g., four times a minute, the momentum of the stranded vessel will, once it is moved, tend to integrate the tension surges so that their effects become cumulative. When as sometimes happens a vessel is stranded in such a manner that it is relatively free for a limited amount of rocking movement, the timing of the tension surges can be adjusted to equal the natural period of the. stranded vessel to obtain an effective amplification of towing force.

Referring now to the drawing and to Fig. 1 in particular, a vessel 10 is shown stranded on a shallow bar 11 in a body of water 12. A power driven ship, such as a tug 13, located in deep. water is suitably connected to the stranded vessel 10 through a tow linev or cable 14 for exerting a, pull or traction upon the vessel 10. After it has been determined by computation or trial that maximum effort by one or more tugs 13, together with whatever aid can be contributed by the propulsion system of the stranded. vessel 10, is unable. to release the vessel 10, a system, for practicing the method of the invention is brought into being- Such a system in its preferred form may comprise a barge device 15 suitably secured to the tow cable 14 at points 16. between the stranded vessel 10 and the tug 13 and provided. with a power plant 17 of a type whichiscapable of furnishing periodic forward thrusts to the tow cable 14 the arrangement being that the'tug- 13, preferably at full throttle, places a high steady tension on the cable 14 while the barge 15 imparts periodic thrusts thereto.

A suitable form wj ichthe power plant 17 may take is. shown diagrammatically in Fig. 2 ascomprising an explosion or combustion chamber 20 closed at its upper end by a dome-shaped. cover 21 and open at the bottom to water when suitably mounted in the floating barge 15. The walls of the combustion chamber preferably consist of a vertical tubular member 22 connected to the cover 21 and to a rearwardly extending tailpipe 23 of suitable length and diameter and preferably having its terminal portion 24 of reduced diameter. Fuel, for example in the form of a combustible mixture of air and high test gasoline, is supplied to the chamber 20 by a fuel injection systemv 25 through a tube 26 and an intake valve 27. These elements may all be of conventional mechanical design. The valve 27 may be operated mechanically or electromagnetically butcis here shown as being biased to closed position by a spring 28 which permits the valve 27 to open under the pressure of the injected fuel when the system 25 is energized by a manually operated switch 29 and a battery 30. Ignition of the combustible mixture in the chamber 20 may be effected by spark-gaps 31 adapted to be connected in the discharge path of a capacitor 32 through a suitable switch 33 here shown as being of the push-button type. Suitable means for exhausting the spent gases from the chamber 20 are provided and may comprise a valve 36 biased to closed po sition by a spring 37 and adapted to be opened manually by means of a bell crank lever 38. Any suitable timing system may be provided for controlling the operation of the switch 29, the switch 33, and the exhaust valve lever 38, but for simplifying the description they have been shown as being manually operated and it is here pointed out that this is entirely feasible since it has been found that in those situations where the invention will probably find its greatest utility, a complete cycle will take ten to twenty seconds.

An operating cycle of the power plant 17 commences with closing of the switch 29 to fill the combustion chamber 20 with a combustible mixture and ends with the exhausting of the burnt gases through the valve 36. When the combustible fuel mixture is ignited in the firing chamber 20 by the spark plugs 31 the water under the chamber 20 and in the pipe 23 is constantly accelerated as the gases expand thereby oppositely accelerating the barge to impart a forward thrust or tension surge on the cable 14 which is being held taut by the tug 13, the driving force (work done) arising from the expulsion of the water from the pipe 23. The propulsive force is proportional to the mass of the expelled water per unit time multiplied by its velocity and hence the efiiciency is increased by reducing the cross section of the terminal portion 24 of the pipe 23. The rearwardly extending pipe 23 directs its expelled water so that it washes around the stranded vessel 10 to disturb the adjacent sea bottom and thereby facilitate release of the vessel 10.

It has been found to be quite important that the steady tension applied to the cable 14 be sufiicient to hold the cable taut so that there is no ill effect due to cable sag. This is evident from an electrical analogue where the smaller the compliance the more efiicient the transmission.

No novelty per se is claimed for the power plant 17 and since a suitable design requires no more than handbook engineering the foregoing description is believed to be sufii-cient to enable anyone skilled in the art to construct a similar device suitable for providing the periodic thrusts to a taut tow line in accordance with the invention. It is of course obvious that dimensions and other parameters will vary with the amount of thrust desired which in turn will depend to some extent upon the size and weight of the stranded vessel and the power of an available tug. To be more precise, the efliort required is a function of the weight of the stranded vessel supported by the sea bottom, i.e., the ground reaction, and the coefiicient of friction of that bottom. Thus, a beached three hundred ton craft would have a ground reaction of three hundred tons, while the same craft would have a ground reaction of one hundred tons if the water it displaces when stranded is two thirds its displacement when afloat.

Under what might be termed average conditions, if the ground reaction of a stranded craft is no greater than 300,000 lbs. and the coefficient of friction is less than 0.8, the craft can be released with a tug holding the tow cable taut under 35,000 to 40,000 lbs. tension in combination with a surge device producing 200,000 lbs. thrusts periodically.

The method of the invention is indifferent to the particular mechanism employed for imparting the periodic tension surges in the stressed towing cable and a number of suitable mechanisms will suggest themselves to one skilled in the art. One such arrangement would be to have the towing cable arranged to unreel from a windlass braked to supply a tension of say 10,000 lbs. (which would enable the tug to continue underway) and periodically greatly increasing the braking force momentarily or, alternatively, the Windlass could be completely stopped for an instant, the increase in tension due to the momentum of the tug being absorbed in and transmitted by the elasticity of the cable.

While for the purpose of disclosing the invention a single embodiment has been described in detail, the principles involved have been made clear enough to enable anyone skilled in the art to incorporate the invention in other obvious embodiments without departing from the scope of the appended claims.

What is claimed is:

1. A releasing apparatus for a stranded vessel including a towing ship and a towing line having its opposite ends connected to the stranded vessel and the towing ship, and, between the stranded vessel and the towing ship, an explosion driven underwater jet device in the said towing line for imparting periodic tension surges to the towing line.

2. A releasing apparatus in accordance with claim 1 wherein the underwater jet device is directed towards and produces a flow of water around the stranded vessel for disturbing the adjacent sea bottom.

3. In a system for releasing a stranded vessel a tow line connected to the stranded vessel, a towing ship adapted to place a substantially steady tension of one order of magnitude on the tow line, and means for periodically producing in the tow line while under tension, tension surges of the next higher order of magnitude.

4. The method of releasing a vessel stranded in shallow water comprising the steps of attaching a tow line to the stranded vessel and to a power driven tow ship in deep water, powering the tow ship at substantially full throttle to place the tow line under high steady tension, and applying periodically to the tow line while it is so tensioned tension surges of at least twice the magnitude of said steady tension.

5. The method of releasing a vessel stranded adjacent to deep water comprising the steps of securing a tow line to the stranded vessel, developing under static tow in the direction of deep water a substantially steady tension in the tow line to hold it taut, and superposing upon such steady tension in the tow line additional momentary tension at regulated spaced intervals of time.

References Cited in the file of this patent UNITED STATES PATENTS 891,352 Merrill June 23, 1908 1,022,771 Church Apr. 9, 1912 1,167,139 Williams Jan. 4, 1916 1,445,839 Mahoney Feb. 20, 1923 

